This application claims the priority of 100 34 442.9, filed Jul. 15, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an electronic unit in a motor vehicle which can detect and protect against polarity inversions in the vehicle electric power supply.
Many electronic units are found in motor vehicles, particularly control units for various motor vehicle functions. In the event of a polarity inversion of the onboard power supply voltage (for example, by an unintentional exchange of the battery pole connections during an external start), very high electric currents may flow. The longer these currents flow, the greater the damage which may occur on control units and/or on other electric and electronic components in the motor vehicle. Heretofore, no measures have been known checking a polarity inversion, and particularly the extent of possible damage by a polarity inversion, in the shop.
It is an object of the present invention to provide a method and apparatus for detecting a polarity inversion of the onboard power supply voltage.
This object is achieved by the method and apparatus according to the invention, in which the voltages present at the connections for the negative and positive on-board power supplies are compared with each other or with reference values. A polarity inversion is detected when the voltage at the negative power supply is greater than that at the positive power supply, or alternatively when the voltage at the negative power supply is greater than a reference value, or the voltage at the positive power supply is less than a reference value. In the event of any such occurrence a polarity inversion is recognized and stored.
Electronic units in motor vehicles, particularly in the form of control units for motor vehicle functions, normally have a connection for the negative onboard power supply voltage, or for connecting to the vehicle mass or the negative battery pole, and a connection for the positive onboard power supply voltage or for connecting to the positive battery pole of a motor vehicle battery. A polarity inversion of the onboard power supply voltage takes place, for example, if, during an external starting attempt, the battery pole connections are exchanged. The positive onboard power supply voltage is then applied to the connection for the negative onboard power supply voltage and vice versa.
By means of the functional block according to the invention, the actual voltage at the connection for the negative onboard power supply voltage is therefore compared with the actual voltage at the connection for the positive onboard power supply voltage. A polarity inversion is detected and the polarity inversion detection is stored if the actual voltage at the connection for the negative onboard power supply voltage is higher than the actual voltage at the connection for the positive onboard power supply voltage.
In a first alternative, the actual voltage at the connection for the negative onboard power supply voltage is compared in the functional block with a defined upper limit value; it is measured, for example, in comparison to a mass uncoupled from the negative onboard power supply voltage. A polarity inversion is detected and the polarity inversion detection is stored, if the actual voltage at the connection for the negative onboard power supply voltage is higher than the upper limit value.
In a second alternative, the actual voltage at the connection for the positive onboard power supply voltage is compared in the functional block with a defined lower limit value; it is measured, for example, also in comparison to a mass uncoupled from the negative onboard power supply voltage. A polarity inversion is detected, and the polarity inversion detection is stored, if the actual voltage at the connection for the positive onboard power supply voltage is lower than the lower limit value.
The three possibilities can also be combined with one another in a meaningful manner. The polarity inversion detection is filed either in the electronic unit itself, for example, in a fault memory, or is emitted, for example, as bus information, to another unit for central storage.
It is particularly important with respect to all three possibilities that the unit has an internal electrical supply unit which can be used independently of the polarity of the onboard power supply voltage and completely independently of the onboard power supply voltage. Such a supply unit may, for example, be a booster battery, an accumulator, a power cap or another capacitor or a circuit which can supply an electrical supply independently of the polarity of the onboard power supply voltage. The reason is that this supply unit must supply the electronic unit with electrical power upon the occurrence of a polarity inversion. A control unit which already contains such a supply unit is preferably used for the electronic unit according to the invention. Such control units are used, for example, in the case of theft warning systems which emit an alarm when the battery is branched off. A supply unit provided for this purpose may optionally be used for the invention.
Preferably, the duration of the polarity inversion is also detected and stored. Also, it is preferable that the actual voltage at the connection for the negative onboard power supply voltage and/or the positive onboard power supply voltage, and/or the difference between the two can be detected at the point in time when the polarity inversion starts (or for the entire duration of the polarity inversion) and can be stored.
By means of the invention, a polarity inversion detection can be queried routinely, for example, by a diagnostic unit in the shop. This also increases the safety and the availability of the vehicles as a result of an early detection of preliminary damage caused by polarity inversion.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.